Control system



June 30, 1942. E. F. DIEKHOFF CONTROL SYSTEM Fild Sept. 26, 1938 2Sheets-Sheet 1 Inventor Earl IF. Diclkhoff Qttomeg June 30, 1942.DIEKHOFF 2,287,788

CONTROL SYSTEM Filed Sept. 26, 1938 2 Sheets-Sheet 2 Fig? 2 3m cntorEarl F. DiekhoIPP duel-neg Patented June 30, 1942 CONTROL SYSTEM Earl F.Diekhoil', Minneapolis, Minn, assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn, a corporation of DelawareApplication September 26, 1938, Serial No. 231,651

17 Claims.

This invention relates to a control system and more particularly to acontrol system to be used in connection with a heating system althoughthe principles of the invention are equally applicable to a coolingsystem.

In all heating systems there is a definite time lag between the timethat a change in operation of the heating system takes place and thetime that this change in operation actually afiects the temperature ofthe space. This time lag is due to the length of time required for theheating medium to actually reach the space, to the heat capacity of thefurnace and to the time required for the temperature of the space beingheated to rise after the heating medium reaches the space, this lattercondition being more particu-.

larly noticeable in a direct radiation system. This time lag will differwith various types of heating systems but such time lag is inherent inall heating systems and this is likewis true in the case of coolingsystems.

Where the heating system is controlled directly in accordance with thetemperature of the space the inherent time lag of the heating systemcauses undesirable fluctuations in the space temperature. Thus where theroom thermostat calls for heat, for example, the temperature of theheating means will rise above that actually necessary to raise thetemperature of the space to the desired value and after the thermostatis satisfied the residual heat in the heating means will continue toraise the temperature of the space beyond the desired value. It has beenfound impractical to construct thermostats without a definite operatingdifferential so that a decrease in temperature in the space will notimmediately affect the operation of the heating system until thetemperature has dropped a certain amount below that at which thethermostat is satisfied as for example 2. If the temperature of theheating means is not raised until the temperature of the space hasfallen this 2 the temperature may continue to fall beyond this valuebefore the change in operation of the heating plant will become apparentin the space by reason of the lag in the heating system. The temperatureof the space will therefore be caused to undershoot and overshoot andwill fluctuate an undesirable amount.

In accordance with my invention I have provided means to both anticipatethe arrival of additional heat in the space and to anticipate a drop inthe amount of heat supplied to the space in a manner to cause thetemperature of the space to be maintained at substantially the desiredvalue. My invention is particularly ap- 55 plicable with a-controlsystem of the so-called floating type. In one form of the invention, aroom thermostat is movable between a pair of relatively fixed contactsand when the thermostat engages the cold contact, the supply of fuel tothe furnace is gradually increased until the thermostat moves away fromthis contact. If the temperature in the space becomes sufiiciently warmso that the thermostat engages the other fixed contact, the supply offuel is gradually decreased until the thermostat moves away from thislatter contact. Heating means are positioned adjacent the thermostat andoperated in such a manner as to anticipate both a rise in temperature inthe space and a drop in temperature in the space so as to maintain thetemperature at a substantially uniform value. In a second form of theinvention, a room thermostat that cooperates with a pair of fixedcontacts located at one side thereof operates the same type of system.

It is therefore an object of my invention to provide a control system ofthe type outlined above for controlling the operation of a heatingsystem in such a manner that an increase in temperature and also adecrease in temperature in the space being controlled is anticipated soas to maintain the temperature of the space at a substantially constantvalue.

Another object of the invention is in the provision of a control systemof the floating type wherein a thermostat which cooperates with a pairof fixed contacts located on one side thereof is provided to control thesystem.

Other objects and advantages will become apparent upon a study of thespecification, claims, and appended drawings wherein are illustrated twopreferred forms of my invention, and wherein Figure 1 is a schematicview of one form of system embodying my invention, and

Figure 2 is a schematic view of a second form of system embodying myinvention.

Referring more particularly to Figure 1 of the drawings, thereference'character l0 represents a space whose temperature is beingcontrolled, there being a radiator i I located in the space forincreasing the temperature thereof, this radiator being connected bypipes I2 and I3 to a furnace H. A pipe 15 is provided by means of whichfuel is supplied to the furnace, the flow of fuel through this pipebeing controlled by a valve I6.

The position of valve l6 and consequently the amount of fuel that issupplied to the furnace may be controlled by a motor generallyrepresented by the reference character 20, this motor vbimetallicelement 66 for this purpose.

being oi versible type. Themotor' is illustrated] a 21 which drivesthrough .the: reduction ggearing 2g. ashaft 29 on whichismount'eda'crank mem m'ean's-oi'the crank arm 32fto thestem 3.3 of the valve l8and as the shaft 2831s moved in one direction or the other by the motor20, the posi honor the crank 30 and the xcrank arm'fl; is; varied tovary theposition lot the valve-member l6. Also carried by the shaft 29is an insulating arm 35- which cooperates with switch members iTheswitch member: 36' includes a 36 and 31. flexible arm 38 having aportion extending'lnto the path of the arm 35 so as to be movedthereby.. The arm 38 carries contacts 39 and 46 and when the arm 38 isin its normal position the contact 39 engages a contact, mounted ontheresilient arm 42. Upon rotation'of crank 35 in a counter-clockwisedirection the arm 38 will be moved upwardly until thecontact 46 carriedThis crank member. is connected by 'f thereby engages the contact on thearm '45.;

The resilience of the arm 42 will cause this arm to move with the arm 38until contact 46 engages'contact 44, and upon further movement of thearm 38 upwardly, the contact 39 is moved The out of engagementwith thecontact switch member 31 includes a resilient arm-"50 having a portionextending into the path of movement of the arm 35, this arm 50 carryinga contact 5| cooperating with a contact 52 carried by the stiff arm 53.,Whenthe arm 35 is rotated in a clockwise direction a suflicient amountthe resilient arm will be flexed downwardly so as to move the contact 5|out o'fengagement with the contact 52. These switches are designed tointerrupt. energiaation ofdthemotor 20 upon movementof the valve l6thereby to its extreme positions as will be explained hereinafterLocated in the space H) being heated is a thermostat which may-comprisea bimetallic ele-. ment 66 carrying an arm Sl -for cooperation with thefixed contact'68 and 69. The-arrangement is such that upon a rise intemperature in the space the bimetal will cause movement of arm 61'towards the contact 69'and upon a drop in tem- 1 perature in the spacethe arm 61 will be moved towards the contact 68. Closely associated-withthe-bimetallic element 66 are a pair ofheaters ashort time'the bimetal66 will be heated sufliciently to move the arm 61 out of; engagementwith the contact 68 whereupon the heater J0 and Hand 1|. These heatersare arranged to rapid- 1y. increase the temperature of '-the bimetallic,element' 66 upon cnergization thereof and if desired these heatersmaybe wound around the These heatersarealso designed to have a lowresidual heat capacity sothat upondeenergization thereof they willcoolrapidly. Y I

For supplying power for operating the. motor 20, a step down transformer15 having a primary 16 connected to a suitable source of power (notshown) and a low tension secondary i1 is provided.

With the parts inthe positions shown, th room thermostat 65 issatisfied, that is, the arm 61 is midway between the contacfs 68 and 69and is neither calling for more heat not for'less heat. The fuel supplyvalve I6 is in a fixed position wherein -it is supplying substantiallythe ZJZB'LYTGU-Y" 4 proper amount-o'ffifuelto. the furna'ce l4,tomaintaih the temperature of. the space at the desire able valueTheheatei flu adjacent 'the'thermm -stat-65 isdeenerg'ized'butthe'hea'ter -ll is ener- .gized. by means of 'the'following circuit:from one side ofthe secondary 1 1 through conductors doctors 84,, -f85.1 the --heate r conductor 86" a resistance elernensl 'l'; andconductor 8.8 tothe other side of the-secondary ,It will be noted heaterincludes 6 thefleld coilv and the-resistance 81 is provided .in thiscircuit sci-thatv the resistance-will be high' enough. to reducethecurrentflow through. the held-coil 24- to:a value which willbe'insufficient that this circuit "through the to rotate; the armature'22.

- 'Assun ie. now that the temperaturewithin the spacegbegins to' fall'due to an increased load on the heating system so that the arm 6] ofthermostat" 65 engages. the contact 68. When this happens, current willflow through the field coil 23 asfollows: from the secondary 11 throughconductor 96, bimetal 66, and. arm 61 of there mostat 65, contact 68,conductor 9|, heater element' 1|]; conductor. 92, switch arm 53,contacts 52 and 5|, switch arm 50, conductor 94, field coil 23, andconductors 8| andv 8'] to the other side of the transformer secondaryTI. The encrgization of the field winding 23 causes rotation of theshaft29 and crank 30 in adirection to gradually move the valve l6towards its wide open position. The Valve |6 will continueto movetowards'this .wide open positionas long asthis field winding 23 isenergized. Should the winding 23 be energized until the valve .IB is inits fully open position the arm 35 carried-by the shaft 29 will open theswitch 31 to deenergize the winding 23 when the valve reaches its wideopen position.

perature of the bimetal 66 'to'increase more rapidly than thetemperature of. the space I0 so as to anticipate the arrival ofheattherein. After the field winding 23 are both decnergized. Deenergizationof the winding 23 stops. operation of motor 23 and the valve|6-thereup0n remains in a further openposition. The deenergization-ofheater llijcauses the temperature'of the bimetal 66 to fall and ifsufficient heat has not arrived in ,the space by this time the bimetal65 may again move the arm 6! into engagementwith the contact 68whereupon the above cycle of oper-' ation is repeated and the valve I6is moved to a.

further open position. The heater 10 by causing the bimetal .66 to heatmore rapidly than the temperature of thespace insures that thevalve 6will always stop operating before the temperature of the space hasactually risen to the desired value, thus substantially reducing thepossibilities vof the space temperature "rising above the desired value.I I

As noted above the heater 1 l'remains energized during all this time sothat the bimetal 66 is slightly above the temperature of the space.Should the space temperature begin to rise above the desired value thearm 6! of the room thermostat will engage the fixed contact 69 whereuponthe field winding 23 cfthe motor 20 will be energized through thefollowing circuit: from the secondary ll of transformer 15 throughconduc- It 4 will be noted that this energizing circuit for the fieldwinding 23 includes the heater I8 and; this heater will accordingly heatup causing the temtor 90, bimetal 66, arm 81, contact 00, conductorsI00, 04, arm of switch 20, contacts 30 and H, arm 42, conductor 02,field winding 24', conductors 0| and 00 to the other side of secondary11. It will be noted that this circuit shunts the circuit through theheater 'II and the resistance 81 so that the current through the heaterII is reduced to a negligible value and this heater will begin to cooloil. The energization of field winding 24 causes operation of motor 20in a manner to move the valve I0 towards its closed position.

Since the heater II which is normally energized is now shunted out bythe circuit through the field winding 24 and begins to cool oi! thetemperature of the bimetal I will drop more rapidly than the temperatureof the space so that the arm 61 will move away from the contact 69before the space temperature has actually dropped to the desired value,in this manner anticipating the drop in temperature before it actualloccurs and thus compensating for the lag in the heating system. In otherwords, although the valve I0 is moved towards closed position thetemperature of the space I0 will not begin to fall immediately becauseof the heat capacity of the radiator. II and furnace i4 so that theirtemperatures will fall, very'slowly. As soon as the arm '1 moves awayfrom the contact 00 the shunt circuit around the heater 'II isinterrupted so that the heater is again energized and since the circuitthrough the field winding 24 now includes this heater and the resistance01 there will be insumcient current flowing through the field coil 24 tocause rotation of the armature 22. If the temperature of the space isstill higher than that desired the arm 61 will move back into engagementwith the contact 00 whereupon the valve It will be moved still furthertowards closed position, the heater II will cool of! and the arm 01 willagain move out of engagement with the contact 60.

Should the valve be moved to its entirely closed position the arm movesthe arm 30- of switch 36 into engagement with the contact 44 and out ofengagement with the contact 4I. when the contact 39 is moved out ofengagement with the contact 4| the circuit through the armature 24 isinterrupted and rotation of the motor therefore stops since the valvehas been moved to its entirely closed position. The movement of contact40 into engagement with contact 44 establishes a new circuit through theheater 1| as follows: from the secondary 'II throughconductor 88,resistance 01, conductor 00, heater 'II, conductors 05, 84, switch armof switch 36, contacts 40, 44, arm 45, conductor I05, resistance I06,and conductors I01 and II to the other side of the secondary 11. Thiscircuit is of course shunted out as long as the arm 01 of thermostat 65is in engagement with the contact 09 but as soon as the arm moves awayfrom the contact the heater will again be energized by means of this newcircuit, the original circuit for this heater being interrupted at theswitch 38. This new circuit includes the resistance I00 which has thesame impedance value as the field winding 24 so that the heat given ofifby the heater II will be substantially the same as-when the,,circuitthrough the heater included the field winding 24 when the thermostatblade 01 moves away from contact 69. It is necessary of course thatheater ll be energized at this time even when the contacts 30 and 4| oflimit switch 30 are opened since'otherwise the thermostat would engagecontact 00 at a higher ambienttemperature than normally, which wouldcause hunting of the system. Since at this time the circuit throughfield winding 24 is open, it is necessary to insert a resistance in thecircuit to the heater II hav-'- ing the same impedance value as thewinding 24 so that the calibration of the thermostat will not be upset,and accordingly the resistance I00 is provided.

It will now be apparent that when the temperature of the space is belowthe desired value and thermostat arm '1 engages contact 00, the valve IIwill move towards open position and the heater II will be simultaneouslyenergized so as to open the circuit at the thermostat and stop theoperation of the valve before the space temperature has actuallyincreased to the desired value so as to anticipate the arrival of heatin the space This operation will occur intermittently until the spacetemperature has risen to the desired value whereupon the arm 61 of thethermostat remains midway between the contacts I and 00. During allthistime the heater II is energized but if the temperature of the spaceshould rise above the desired value thermostat arm 01 will engage thecontact II energizing the motor 20 in a manner to move the valve l0towards closed position and simultaneously shunting out the heater II sothat the temperature of the bimetal will drop more rapidly than thetemperature of the space so as to anticipate the fall in temperature ofthe space so that the valve II will not be closed too far. This valvewill be intermittently closed in this manner until the temperature ofthe space has dropped to the desired value wherein the arm 61 will againbe maintained between the contacts 00 and 00 and the heater II, when inthis'posltion, will be energized. The valve I I is accordingly moved toa position: wherein the proper amount of fuel is supplied to the furnaceto maintain the temperature of the space at substantially the desiredvalue and this is done while preventing overshooting or undershooting ofthe space temperature to any appreciable extent by means of the novelarrangement of the heaters I0 and II.

Referring now to the form of invention shown in Figure 2, the motor 20for operating the valve I 6 is controlled by a relay generallydesignated by the reference character III. This relay includes an arm II I cooperating with the fixed contacts H2 and H3. The relay alsoincludes an armature composed of members H4 and H5 and cooperating withthe armature member H5 is a relay coil I I6. When energized this coiltends to move the arm III about the pivot II'I into engagement with thefixed contact H3. A second relay coil I I8 cooperates with the armaturemember H4 and when coils H0 and III! are simultaneously energized theyexert equal and opposite forces on the two armature members and tend tomaintain the arm III midway between the contacts 2 and III. A thirdrelay coil I20 also cooperates with the armature member H4 and when boththe coils III! and I20 are energized the armature member H4 is urgedupwardly. these two coils more than counteracting the effect of therelay coil IIi whereupon the arm II I is moved into engagement with thefixed contact H2.

The operation of relay H0 is controlled by a room thermostat I25 whichdiffers from the room thermostat of Figure 1 in that the fixed contactsare both d sposed on the same side of the movable arm of the thermostat.This thermostat is shown to comprise a bimetallic element I26 on themovable arm I21 of which'iscarried thecontact.

members I28 and. I29. Fixed contacts I30 and I former I46, throughconductor'I60, arm III, con- I3I cooperate with the contact members I23and I I29 and thearrangement is such that upon'an .initial drop intemperature contact member I28 engages the contact I30, and upon afurther drop .in temperature affecting thethermostat the contact' memberI29 engages the fixed contact I3I.

- As the temperature affecting the thermostat rises;

I the contact members move away from the fixed contacts in the reverseorder. ,adjacent the bimetal I26 are the heaters I35 and I36. Theseheaters may, if desired, be wound Disposed closely around the bimetal.Heater I36 is arranged to be energized when thecontact member I28 is inengagement with the'fixed "contact I30 and the heater I35 is arranged tobe energized when the con'tactmember I29 engagescontact I-3 I.

" Power is "supplied to the relay II6 by, means I' fthestep-d ntransformer- I40 composed of 'f, the low.tension secondary MI and aihigh tension -primary I42 connected to the line wires I43 and I44which-are,- in turn, connected to a' suitable source ofpower','notshown.', l-For'supplying power 1 to the motor 20 a step-down;transformer I46 may be provided, this transformer including the 4 low'tensi'onsecondary I41 'andthe high tension I48 connected, to the linewires I43 and 4.5". M U

."- f Operation of Figure 2 Whe n the temperature in the-space'is at thedesired value, the contact member I23 of the thermostat,I25 will be inengagement with the jfixedrcontact I30 whereupon current will flowthrough the heater I36 and the relay coil I I8 as follows: from thesecondary I4I of'transformer 140 "through conductor I50, variableresistance V II, conductor I52, bimetal I26, contact member,

I28; fixed contact I30, conductor I53, electrical heater. I36, conductorI54, relay coil M0, and

conductors I55 and I50 to the other side of the secondary MI.Accordingly, some heatwill be 'suppliedto thethermostat by the. heaterI30 whereby the temperature ofthe bimetal will be somewhat abovethespacete'mperature. It will I benoted' that the relay coil Ila-is at thistime energized, but relay coil 6 is always energized through thefollowing circuit: from the trans-- former secondary MI; throughconductor I60,- variable resistance;I6I,,conductor I;62,'re1ay coil- ',II6, and conductors I55 and' I56 to the other side of the f;secondary-I4I1 The, relay coils I16 and I IBare so designedand the current flowthrough the-two members'are adjusted by means of the variable-resistance,I 6I so that-when these two j coils are energizedand the relay coil I20is not energized, they .Will' attract the armaturehmem bersf l I I-and 5equally So that'the arm III will be in a position midway. of thecontacts H2 and I I,'I'3. At;this time'there is' no flow of; currentthrough'the motor 20 so that the valve I6 isin a 'fixed position andsupplying afixed amountof T tact II3, conductor I6I, limit switch I62,conductor I63, field winding '24, and conductor I64 to the other side ofsecondary I41. Energization of ,winding 24 will cause the motor 20 togradually move the valve I6 towards-closed position thus decreasing thesupply of fuel to the furnace and in this manner reducing thetemperature'in the space. Since the heater I36 is no longer energized,the temperature of the thermostat will fall somewhat more rapidly thanthe temperature of the space and'in this way the thermostat willanticipate the drop in temperature in the space by reason of thereduction in the sup plyof fuel to the furnace, and when the thermostathas cooled sufficiently so that the circuit through arm 'I 28 andcontact I30 is reestablished,

, thecircuit through the motor 20'will be interrupted by the relay IIOand the heater I36 will again be energized.

If new the temperature in the space'sho'uld fall sufiicientlyso that themember I29 of the thermostat I ismoved into engagement with the contactrelay coil II6, the energization of the coil I20 will provide sufficientextra attraction for the armature member II4 so that the. arm III willbe'moved into engagement with the contact II2.

, A circuit is now established through the field winding 23 of the motor20 as follows: from the transformer secondary S41 through conductor I60,arm III, contact H2, conductor I10, limit switch Ill, conductor I12,field'winding 23, and

conductor I64 to the other side of transformer secondary I01.Energization of the winding 23 causes the motor 20 to move the valve I6towards open position 1 whereupon the supply of fuel to the furnace isincreased so that additional heat is supplied to the space to raise thetemperature thereof.

Since the heater I is now energized and the heater I36 is-stillenergized, additional heat is supplied to the bimetal I26 to furtherincrease the temperature-thereof abovethe space temperature and in thisway t anticipate the arrival-offadditional heatin the space. Accord--ingly, the contact member I29 will be moved out of engagement with thecontact I3I prior-to the time that the space temperature has actuallyrisen to the desired value So as to compensate for .thelag in' theheating system, and when this happens the arm III of the relay IIO willagain I move into a position between the contacts II2 fuel tothefurnace. a Assume now that the tem- 1 pera'ture' within the spacerises higher than is desirabl'e. In this case, thebim'etal 26 'will,move

member I 28 out. of engagement with the contact I30, thus interruptingthe aforedescribed circuit through the relay coil H0 and the heaterI36..

j Since the relay coil II6=is always' energizedzand T since at this timeneither-coil. I'I8nor I20'is eri- 'erg ized; arm 'III: will-be movedinto engagementwith the contact: ,I I3, thus completing-aicircuitfthrough-'the'field winding"2,4 of the motor- 20. as follows: from thesecondary: I41offthe transand H3 so that the circuit through the motor20 will be interrupted and the movement of valv IB-will cease.v I Itwill now be understood that'the formof inventionillusjtrated'in Figure 2operates in substantially the same manner as theform of. in-

' vention shown in Figure 1 except that a differcut type of thermostatis employed to control the operation of motor 20, thefixedcontacts ofthis thermostat being placed on one side of the movable armithere'ofjandthe thermostat controlling th'eqoperation of motor 20 through the relay'0.

It will be understood that the limit switches I62 and Ill function inthe same manner as the limit switches of Figure 1 to interrupt thecircuit through the motor whenever the motor moves the valve to eitherof its extreme positions.

The provision of the adjustable resistance |5l permits adjustment of theheating capacities of the heaters I and I36 and if the current throughthese resistances is varied by means of this adjustable resistance, thecurrent through the relay coils H8 and I20 will likewise vary andaccordingly the adjustable resistance IGI is employed to likewise adjustthe current flow through ,the relay coil 6 so that the relay coils H6and ill will exercise equal effects on the armature members H4 and Hi.It should be understood, of course, that the heating eflects of theheaters in Figure i may likewise be adjusted by the provision ofsuitable adjustment resistances as in Figure. 2 so that the heatingeiTects of these resistances may be adjusted to suit the needs of theparticular heating system.

Having described the preferred forms of my invention, many modificationsmay become apparent to those skilled in the art. For example, the motor20 instead of operating a fuel valve, may operate check and draftdampers which regulate the temperature maintained in the furnace or anyother suitable mechanism for controlling the temperature of a space. Thefurnace may be hot water, steam, or a hot air furnace whereupon theradiator ll would be replaced by a warm air duct. In such a furnacethere is a smaller heating lag and the resistances I8 and 'H wouldtherefore have a smaller heat capacity, Any known type of heatingsystemmay be similarly controlled. The room thermostats may also be of anyconventional construcmovement of said circuit controlling means to thefirst circuit controlling position for causing energization of both ofsaid auxiliary heating means, means responsive to movement of saidcircuit controlling means to the second circuit controlling position forcausing energization of one only of saidauxiliary heating means, and

means responsive to movement of said circuit controlling means to thirdcircuit controlling position. for interrupting operation of both of saidauxiliary heating means.

3. In a system of the class described, temperature responsive meansincluding a control arm movable in response to variations in the ambienttemperature, spaced contacts arranged to be engaged by said arm inresponse to movement thereof in opposite directions, heating means inclose proximity to said temperature responsive means for raising thetemperature of the temperature responsive means above the ambienttemperature, means for causing operation of said heating means at highcapacity when said control arm is in engagement with one contact, meansfor causing operation of said heating means at low capacity when saidcontrol arm is in engagement with neither contact, and means forinterrupting operation of said heating means tion wherein thetemperature responsive element only by the scope of the appended claims.

I claim as my invention:

1. In a temperature controlling system, a temperature responsiveelement, a circuit controlling means carried by said element and movableinto first, second and third circuit controlling positions in responseto variations in the ambient temperature for controlling temperaturechanging apparatus for a space whose temperature is to be controlled,auxiliary meating means having fixed high and low capacities locatedclosely adjacent said temperature responsive element, means responsiveto movement of said circuit controlling means to the first circuitcontrolling position to cause operation of said auxiliary heat ing meansat the fixed high capacity thereof, means responsive to movement of saidcircuit controlling means to the second circuit controlling position tocause operation of said auxiliary heating means at the fixed lowcapacity thereof, and means responsive to movement of said circuitcontrolling means to the third circuit controlling position to interruptoperation of said auxiliary heating means.

2. In a temperature controlling system, a temperature responsiveelement, a circuit controlling means carried by said element and movableinto first, second andthird circuit controlling positions in response tovariations in the ambient temperature, a pair of auxiliary electricalheating means located closely adjacent said temperature responsiveelement for raising the temperature of the temperature responsiveelement above when said control arm is in engagement with the. othercontact.

4. In a system of the class described, temperature responsive means forcontrolling the operation of heating apparatus, said temperatureresponsive means including a control arm movable in response tovariations in the ambient temperature, spaced contacts arranged to beengaged by said arm in response to movement thereof in oppositedirections, a pair of auxiliary heaters in close proximity with saidtemperature responsive means, means for energizing both of saidauxiliary heaters when said control arm is in engagement with one ofsaid contacts, means for energizing one only oi!v taid auxiliary heaterswhen said control arm is in engagement with neither of said contacts,and means for interrupting the operation of both of said auxiliaryheaters when said control arm is in engagement with the other of saidcontacts.

5. In a heating system, heating means for a space, control means forvarying the heating efiect of, said heating means, temperatureresponsive means in said space, local heating means having fixed highand low capacities adjacent said temperature responsive means, meansresponsive to movement of said temperature responsive means to a firstposition in response to a drop'in temperature in the space to causeoperation of said control means to continuously increase the heatingeffect of said heating means and to cause operation of said localheating means at the fixed high capacity thereof, means responsive tomovement of said temperature responsive means to a second position inresponse to a rise in temperature at the temperature responsive meansfor interrupting operation oi said control means and for causingoperation of the local heating means at the fixed low capacity thereof,and means responsive to movement of said temperature responsive means toa third position in response to a further rise in temperature at thetemperature responsive means to cause operation of the control means tocontinuously decrease the heating effect of said heating means and tointerrupt the operation of said local heating means.

the ambient temperature, means responsive to 15 6. In a heating system,heating means for a space, control" means for varying the heating ef-Hfect'of saidjheat'ingmeans; temperature respon- I sive meansinsaid.space,- apair of electrica1,heat'- ers adjacent said; temperatureresponsive "means; said temperature responsive 'mea'ns, heingjmov- Iable between first and second positions zi n1;responseto variationsintemperature at'said means. I means "responsive to movement of-saidtemperature responsive means to the first position vior energizing bothof said electrical heaters and for operating the controlmeansftoflcontinuously in,- crease the :heati-ngefiec't of the.heating-means,

meansresponsive to movementhf the, tempera-i ture responsive means to apositionintermediate said first and secondpositions tooause'energization of one-only of saidelectrical'heaters and. to,

I interrupt operation'jof said "control means, and means responsive tomovementofithe-tempera ture responsive means to {the second position fora causing operation of neither of said electrical heaters and foroperating said control means to the heatingefiect of said ringe1ements." v i 10. Ina heating'system; heating means "for-a; space'co ntr oLmeans; vfor varying the heating efiectfiof ,saidheating means,temperature re-'" sponsivemeans in, said space}means-responsive tomovement of saidf ternperature responsive means to a first positiontooperate, the control means i'n a manner to increase the heating effect:(of the heating means, means responsive to move-. j K ment of saidtemperature responsive'means to a second p sition. spaced. from thejfirst position to] v operatethe control'rneans in a ma n in 5continuously decrease heating means.

, 75 11 a heating system, r'neansfor heating a space, temperatureresponsive means-I in said space, spaced contacts cooperating-"withsaidtern-1 perature responsive means, onejof' said'contajc'ts; beingarranged to becontacted by saidtemperae f ture responsive meanswhen thetemperature affectingthe temperature responsive meansjdrops' toapredetermined -value-, the other contact'-being arrang'edtobeccon-t'acted'by saidtemperature responsive means when" the temperatureaflectingl 'l the temperature r'es'po'nsive'ineans' rises to" a-pre- 85v auxiliary. heating meanshaving fixed high and",

. low capacitiesadjacent the temperature responsive means'forraising thetemperatureof the. temperature responsiveme'a'ns above the ternperatureof the spaoameans responsive to movedetermined value, means responsivetoqengagemerit of said one scontactua-nd' the tem'peraturefl responsivemeans for increasing the heating efiect of said heating means,means-responsive to engagementof said. other Contact and th'etem'perature'responsivemeans for decreasingthe means responsive tomovementofsaid t'emperae. I ftu're responsive m'eans'out of engagement;with' both of said contacts to cause operation'ofzsaid- -."auxil iarvheating means atlowcapa'city, j and V 'means responsive to engagement'of said temp'era ":ture'respohsive rneans'with'saidother 'eontact toi ainterrupt operation. of said ,auXiliaryheatix'rg i meansr .f-f, 1'

' '9; Ina system'of the class'described} tempera-- tureresponsive meansincludinga control ele--- m'ent movablelhetween first and 'second'positions in response to temperaturechanges' affecting the temperatureresponsive means, a pair of electrical heating-"elements adjacent "saidtmpera'ture-re'-f 15, sponsive means, me'ansfor connecting-one ofsaid i"of the position; of "said controlz-element, means 1 connecting said.other heating element to'isaid source "of-power only when; ,said controlelement 1201s in the first position, and means responsiv'etoheating;effect ofsaid heating means, 'apair oi a electric heatersclosely -a'ssociated vwith said terntions for causing .:energization ofboth heaters when the temperature responsive means is in en-.perature-responsive means,- and circuit connecgagement'with-saidonetcontac t, for causing ention of both heatersi when vthetemperatureresponsive means iss-inengagement with said other contact.

8. In'a1heating;system; for heating a perature. responsive means, one;of said contacts being arranged to be contacted by said ternperaiergization of one only of said heaters when said temperatureresponsive) means is in engagement with neither-contact, and forinterrupting opera- ;side of said control arm and. arranged to' besequentially.v engaged thereby in response toan ture responsive ,meanswhen thetemperature ar f eeting the temperature,responsive means.'fdro'ps to a",predetermined-"value; the other contact her-T in'garranged to becontacted by saidtemperature responsive meanswhenthe-ter'nperature afiecting,

the temperature responsiv'e means rises toa' predetermined value; meansresponsive to engagement of said one contact, and, the. temperatureresponsive means for increasing the heatin I ety feet of said heating-means, means responsive to engagement of said other contact and} the;tem- I perature fresponsive; means 'for decreasing the 1 heating effectof said heating means,' auxiliaryz heating means .-closelyassociatedwith said ternperature: responsive; means, means responsive'"to engagement of'said temperature re'sp'onsive' meansv with, said' onecontact-[for ..causing,.oper'ationof a said au rilia'ry' heatingf mean'sat high icapacityf heating elements to-a source of power regardlessmovement of the control element vto the second crease the heating effectof the heatingm'ean's first position for causing operation of saidauXiL- iary' heating means at the fixed high capacity thereof,'mean'sresponsive to movement or the 'ternperature,- span ofcontact's'located-at one increase in temperature affecting thetemperat'ure responsive means, heating means in close proximity tosaidtemperature responsive means a @for raising-the temperatureof thetemperature'- responsive-"means above the ambient. tempera ture, meansfor causing-operation of the heating lmeans at; high capacity when'saidcontrol arm is in engagement with bothpontacts, means-for causingoperation of said heating means at low capaciti when said control arm isin engagement with'onlyone contact; said heating means -being is inengage deenergized' when said control arm mentivith neithercontact. r

.f12. In. a heating system, means for heating a space, temperature;responsive means insaid, "spacega pair d f-contacts cooperating withsaid 'ten perature' responsive means and arranged 'to- Qbe'sequentia-Hyengaged thereby in'f'responseto a position for shunting out saidoneof'theheat-i temperature]responsive'means to a position be-, tween'thefirst andsecond positions for causing- .operation. of: the auxiliaryheating means at the i 1 sfixed low capacity thereof, and meansresponsive to movement of the temperature responsive means to the secondposition for interrupting operation of the auxiliary'heating means. 1

.311. "In a system of'theclass described, temperature responsivemeansin'cluding a control arm" movableinresponse to variationsin theambient .rise in temperature in the space, means responsive toengagement of both of said contacts by said temperature responsive meansfor increasing the heating eflect of the heating means, means responsiveto movement of said'temperature responsive means out of engagement withboth contacts for decreasing the heating eiiect of the heating means, apair of electric heaters closely associated with said temperatureresponsive means, and circuit connections for causing energization ofboth or said heaters when both of said contacts are engaged by thetemperature responsive means, for causing energization of only oneheater when only one of the contacts is engaged by the temperatureresponsive means, and for interrupting energization of both heaters whenneither contacts is engaged by the temperature responsive means.

13. In a system of the class described, condition changing means, meansfor controlling the condition changing effect of the condition changingmeans, said controlling means including a reversible motor means, meansresponsive to a condition being controlled, said condition responsivemeans including a control arm movable sequentially into and out ofengagement with a pair of fixed contacts located on one side of saidcontrol arm in response to variations in the condition being controlled,means responsive to engagement of said arm with both contacts forenergizing a circuit through said motor means to cause rotation thereofin one direction, means responsive to movement of said arm out orengagement with both of said contacts for energizing a second circuitthrough said motor means to cause rotation thereof in the otherdirection,

and means responsive to engagement of said arm with one only of saidcontacts for deenergizing said motor means regardless of the positionthereof.

-14. In a system of the class described, temperature changing means,means for controlling the temperature changing effect of the temperaturechanging means, said means including a reversible motor means, meansresponsive to the temperature of a space being heated by the temperaturechanging means, said temperature responsive means including a movablecontrol arm cooperating with a pair of sequentially engageable contactspositioned on one side thereof, means responsive to engagement of saidarm with both contacts for energizing a circuit through said motor meansto cause rotation thereof in a direction to decrease the heating effectof the heating means, means responsive to movement of said arm out ofengagement with both of said contacts for energizing a second circuitthrough said motor means to cause rotation thereof in the otherdirection, and means responsive to engagement of said arm withone onlyof said contacts for deenergizing said motor means regardless of theposition thereof.

15. In a system of the class described, temperature changing means,means for controlling the temperature changing effect of the temperaturechanging means, said means including a reversible motor means, meansresponsive to the tem-- perature of a space being heated by thetemperature changing means, said temperature responsive means includinga movable control arm cooperating with a pair or sequentially engageablecontacts positioned on one side thereof, means responsive to engagementof said arm with both contacts for energizing a circuit through saidmotor means to cause rotation thereof in a direction to decrease theheating effect of the heating means, means responsive to movement ofsaid arm out of engagement with both of said contacts for energizing asecond circuit through said motor means to cause rotation thereof in theother direction, means responsive to engagement of said arm with oneonly of said contacts for deenergizing said motor means regardless ofthe positions thereof, and heating means located adjacent thetemperature responsive means for raising the temperature thereof abovethe ambient'temperature, said heating means including a first heater inseries with one of said contacts and a second heater in series with theother of said contacts so that the heat imparted to the temperatureresponsive means by said heating means will depend upon how many of saidcontacts are engaged by said control arm.

16. In a system of the kind described, a control element movable betweena pair of spaced contacts, a first coil when energized biasing saidelement toward one contact, a second coil when energized exactlycounteracting the biasing effect of said first coil, a third coil whichwhen energized with the second coil biasing said element into engagementwith the other contact even though the first coil is energized, meansconstantly energizing the first coil, and means for selectivelycontrolling the energization of said other coils.

17. In a system of the kind described, a control element movable betweena pair of spaced con-.

tacts, a first coil when energized biasing said element toward onecontact, a second coil when energized counteracting the biasing effectof said first coil, a third coil which when energized with the secondcoil biasing said element into engagement with the other contact eventhough the first coil is energized, means constantly energizing thefirst coil, means controlling the energization or said other coils, saidlast named means including a condition responsive device having an armmovable in response to variations in a condition being controlledtowards and away from a pair of sequentially engaged contacts located onone side thereof, means responsive to engagement of 'said arm and one ofsaid contacts for energizing said second coil whereby the controlelement is in engagement with neither contact, and means responsive toengagement of said arm with both contacts for energizing the second andthird coils whereby the control element is moved into engagement withsaid other contact.

EARL F. DIEKHOFF.

